We observed that a common source of perceptual errors in the outputs produced by NNST-D, NNST-Opt, and other methods, is when a region with a single color in the original content is mapped to multiple colors in the output (see the first two rows of Figure REF ). However, after converting our outputs to Lab colorspace, we observed that the luminance channel generally matches the target style well, and was free of artifacts. This motivated our post-processing step, which is to take the luminance generated by NNST-D or NNST-Opt, but discard the AB channels and replace them with slightly modified AB channels from the original content. In order to match the content's original AB channels to the generated L channel we perform bilateral filtering [1]}, [2]} on the AB channels guided by the L channel. Then we match the mean and covariance of color distribution formed by the output's L channel and filtered AB channels to the style's color distribution. (see the bottom section of Figure REF ). This has some similarity to the color control proposed in [3]} (which suggests disentangling style from color by inheriting hue and chroma from the content image), but our addition of bilateral filtering helps outputs' final color to better conform to edges present in the luminance, and moment matching enables stylizations which more closely match the palette of the target style.
